Rotary piston engine



July 30, 1968 H, HANTZSCHE ETAL 3,394,877

ROTARY PI STON ENG INE Filed Dec. 15, 1966 FIG. 1 FIG. 2

INVENTORS HELMUT HANTZSCHE et 0| United States Patent 3,394,877 ROTARY PISTON ENGINE Helmut Hantzsche, Meiningen, and Hellmut Uhlig, Walter Muller, Werner Lang, and Karl Heinz Bruckner, Zwickau, Germany, assignors to VEB Sachsenring Automobilwerke Zwickau, Zwickau, Germany Filed Dec. 15, 1966, Ser. No. 602,039

6 Claims. (Cl. 230-145) The present invention relates to rotary piston engines.

In particular, the present invention relates to the inner surface structure of the outer housing of a rotary piston engine and the structure of the slidable sealing elements which are carried by a rotary piston and which slidably engage this inner surface structure of the engine housing.

The invention is particularly applicable to rotary piston engines which have an outer housing which preferably is made of a light metal.

In order to reduce the wear between the inner surface of such a housing and the slidable sealing elements of the piston which engage this inner surface, so as to increase the operating life of the rotary piston engine and so as to achieve good sliding and sealing properties between the inner surface of the housing and the sealing elements of the piston, in a manner similar to the cooperation between the pistons and cylinders of a reciprocating piston engine, it is known to provide at the inner surface of the rotary piston engine housing a deposit of a material which is different from that of the remainder of the housing. This inner surface structure which is different from that of the remainder of the outer housing can be achieved, for example, by chrome plating the inner surface of the housing or by hard chrome plating the inner surface thereof, by flame or electric-arc metal spraying onto the inner surface of the housing, or by pressing into the housing a harder layer of hardened steel to be come situated within and form the inner surface of the housing which otherwise can be made of a light metal.

Furthermore, it is known to reduce the wear between the inner slide surface of the housing and the sealing elements which slidably engage this inner surface by combining with the particular material used for the inner surface of the housing a material for the sealing elements of the piston which is correspondingly suitable for cooperation in a slidable manner with the inner surface of the housing.

Particularly good results have been obtained up to the present time by using for the inner surface of the engine housing a galvanic hard chrome plating combined with hard carbon sealing elements carried by the piston and slidably engaging the hard chrome plating at the inner surface of the engine housing.

Of the presently known methods for improving the inner surface of the engine housing the galvanic hard chrome plating and the combination thereof with hard carbon sealing elements of the piston is still the best and most advantageous solution to the problem.

However, the galvanizing of the inner surface of the housing of a rotary piston internal combustion engine is extremely expensive because of the ditficulties resulting from the configuration of the housing which is in the form of a double lobed epitrochoid. It is only possible to provide the coating at the inner surface of the housing under the most unfavorable technical and economic conditions. In particular, in order to achieve an inner surface layer of hard chrome plating large expensive installations and operations are required. Thus, in order to provide a layer whose thickness is 0.3 mm. operations requiring a duration of 9-12 hours are essential. This means that a considerable amount of cycle time is required for mass production manufacture and in addition there is an extremely high consumption of electric energy.

Furthermore, the use of hard carbon sealing elements 3,394,877 Patented July 30, 1968 "ice for the piston, the strength of which is less than that of metal sealing elements, is unfavorable even from .the stand-point of mounting and repairing the sealing strips which are carried by the piston, since these hard carbon sealing strip are easily damaged.

Furthermore, the manufacture of these sealing strips is extremely expensive, as compared, for example, with cast iron sealing strips, because the hard carbon sealing strips have only a relatively small resistance to bending. As the operating time increases, the hard carbon sealing strips become brittle and break, particularly at edges.

Furthermore, the pressing of a hard layer of high quality material forming a separate individual element and manufactured separately and pressed by means of a suitable pressure into a corresponding manufactured housing adapted to receive the inner layer of hard wearing material requires extremely complex manufacturing procedures which exclude the possibility of an economically feasible manufacture. Furthermore, when such a hard layer of material is pressed into the housing, because it is not homogeneously joined with the light metal of the housing, the heat transfer between the light metal of the housin g and the harder insert is very poor.

A maximum resistance to wear for the inner surface of the housing also is not achieved if it is attempted to improve the inner surface of the housing by the use of flame or electric-arc metal spraying, since because of the melting temperature of the metals used for this purpose it is not possible to achieve an inner layer of the desired hardness.

It is accordingly a primary object of the present invention to provide the inner surface of the housing of a rotary piston engine with a hard-wearing material which will avoid the drawbacks referred to above.

In addition, it is an object of the present invention to provide in combination with the particular material used for the inner surface of the housing sealing elements for the piston made also of a particular material which is especially suited for cooperation with the particular inner surface material of the engine housing.

Thus, it is an object of the invention to combine for the inner surface of the housing and for the sealing elements of the piston materials which will be equal to the requirements of such a construction, with respect to the low degree of the wear resulting from slidable engagement between the sealing elements and the inner housing surface, so as to provide from these constructions a wear of the inner surface and the sealing elements as well as of the combination thereof which will make possible a steady stable running of the piston in the housing of the rotary piston engine.

It is particularly an object of the invention to provide features of the above type which are suited for use with an engine housing made of a light metal.

In accordance with the present invention it has been found best to provide at the inner surface region of the outer engine housing an intermediate layer joined to outer wall structure of the housing and also joined to an inner surface layer, the intermediate layer being made of gas carburized tungsten carbide having a grain size of less than 40 m, having a carbon content of 22.7%, and joined to an outer layer also made of tungsten carbide, with the outer layer having a cobalt additive of 10-20% and a grain structure 60% of which has a micro hardness in the region of 640-783 tons/sq. in. In accordance with a further feature of the invention, the structure of these intermediate and inner layers is determined by the characteristics of deposition of these materials at the inner surface of the housing by means of a plasma arc torch, and the setting of the plasma arc torch, according to a further feature of the invention, remains unchanged during deposition of both of the tungsten carbide layers.

3 Thus, particular note should be taken of the fact that the tungsten carbide changes its chemical composition within the spray gun as a result of the action of the stream of plasma, so that the sprayed layers of tungsten carbide no longer correspond to the initial material introduced into the gun to be sprayed therefrom, and the wear-resistance of these layers is in part dependent upon the sintering of particles of the layers together. The fraction of harder layer material, the microhardness of which is equal to 1423 tons/sq. in. and more, must be 4% or less, and must have a relatively low porosity.

It has been found that when this inner surface construction of the engine housing is combined with piston sealing elements made from ductile cast iron having a tensile strength of 43 tons/sq. in., the best possible operating conditions are achieved.

The invention is illustrated by way of example in the accompanying drawings which form part of this application and in which:

FIG. 1 is a fragmentary partly sectional elevation schematically illustrating the structure fo the invention, the upper sectional part of FIG. 1 being taken along the line of 11 of FIG. 2 in the direction of the arrows; and

FIG. 2 is a schematic sectional view of the structure of FIG. 1 taken along line 22 of FIG. 1 in the direction of the arrows.

Referring to the drawings, the outer engine housing 1 is illustrated therein as having the double epitrochoid configuration which is characteirstic for these engines and which is shown most clearly in FIG. 2 in cooperation with the rotary piston 5.

This rotary piston 5 carries the sealing elements 6 which slidably engage the inner surface 2 of the housing 1, and this inner surface 2 is formed by the tungsten carbide intermediate layer 3 and the tungsten carbide inner layer 4 in the manner described above.

What is claimed is:

1. In a rotary piston engine, an outer housing having an inner surface and a rotary piston situated in said outer housing and carrying sealing elements which slidably engage said inner surface of said outer housing, said housing having in the region of its inner surface an inner layer, which is slidably engaged by said sealing elements, an intermediate layer joined to said inner layer, and a wall structure joined to said intermediate layer, said intermediate layer being situated between said wall structure and inner layer and being made of gas-carburized tungsten carbide having a granular size which is smaller than ,um., having a carbon content of 22.7%, and said inner layer being tungsten cabide having a cobalt additive content of 1020% and made up of grains of which have a microhardness of appoximately 640-783 tons/sq. in. with a fraction of harder layer material, of 1,423 tons/ sq. in. and more, constituting a maximum of 4%.

2. The combination of claim 1 and wherein said sealing elements are made of ductile cast iron having a tensile strength of 43 tons/ sq. in.

3. The combination of claim 2 and wherein both of said layers have a structure resulting from deposition of said layers by means of a plasma arc torch.

4. The combination of claim 3 and wherein the structure of said layers is provided by way of deposition from a plasma arc torch whose setting remains the same during deposition of both of said layers.

5. In a method for providing a rotary piston engine with an inner surface srtucture at the interior of its outer housing adapted to be slidably engaged by sealing elements carried by a rotary piston in said housing, the steps are applying to the inner surface of the housing by means of a plasma arc torch at a given setting an intermediate tungsten carbide gas-carburized layer having a granular size which is less than 40 ,am. and having a carbon content of 22.7%, and, without changing the setting of said plasma burner, applying to said intermediate layer an inner tungsten carbide layer having a cobalt additive of 10-20% with grains 60% of which have a microhardness of approximately 640-783 tons/sq. in. with a fraction of harder layers of 1,423 tons/sq. in. and more being a maximum of 4%.

6. The combination of claim 1 and wherein said housing is composed, inwardly of said intermediate layer, of a light metal.

References Cited UNITED STATES PATENTS 3,033,180 5/1962; Bentele 103130 3,102,518 9/1963 Anderson.

3,128,710 4/1964 Blomgren et a1.

3,155,313 11/1964 Bentele 230- 3,360,191 12/1967 Yamamoto 230145 FRED C. MATIERN, JR., Primary Examiner. W. J. GOODLIN, Assistant Examiner. 

1. IN A ROTARY PISTON ENGINE, AN OUTER HOUSING HAVING AN INNER SURFACE AND A ROTARY PISTON SITUATED IN SAID OUTER HOUSING AND CARRYING SEALING ELEMENTS WHICH SLIDABLY ENGAGE SAID INNER SURFACE OF SAID OUTER HOUSING, SAID HOUSING HAVING IN THE REGION OF ITS INNER SURFACE AN INNER LAYER, WHICH IS SLIDABLY ENGAGED BY SAID SEALING ELEMENTS, AN INTERMEDIATE LAYER JOINED TO SAID INNER LAYER, AND A WALL STRUCTURE JOINED TO SAID INTERMEDIATE LAYER, SAID INTERMEDIATE LAYER BEING SITUATED BETWEEN SAID WALL STRUCTURE AND INNER LAYER AND BEING MADE OF GAS-CARBURIZED TUNGSTEN CARBIDE HAVING A GRANULAR SIZE WHICH IS SMALLER THAN 40 UM., HAVING A CARBON CONTENT OF 2-2.7%, AND SAID INNER LAYER BEING TUNGSTEN CABIDE HAVING A COBALT ADDITIVE CONTENT OF 10-20% AND MADE UP OF GRAINS 60% OF WHICH HAVE A MICROHARDNESS OF APPROXIMATELY 640-783 TONS/SQ. IN. WITH A FRACTION OF HARDER LAYER MATERIAL, OF 1,423 TONS/SQ. IN. AND MORE. CONSTITUTING A MAXIMUM OF 4%. 